Well, they tried multiple times! Some tried a direct image, some tried a compact hash of images that should be known in advance ("Coded Hashes of Arbitrary Imag

Well, they tried multiple times! Some tried a direct image, some tried a compact hash of images that should be known in advance ("Coded Hashes of Arbitrary Images"), another tried a direct mapping to Wikidata entities ("QID emojis"). They ultimately failed because... yeah, they would have been much more difficult to implement than what we have right now.